wifi: brcmfmac: Remove unused brcmf_cfg80211_get_iftype()

brcmf_cfg80211_get_iftype() has been unused since 2013's commit
5cd51c2b ("brcmfmac: Find correct MAC descriptor in case of TDLS.")

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20241004004252.470836-1-linux@treblig.org